title: Patterns of sperm damage in Chernobyl passerine birds suggest a trade-off between sperm length and integrity.
abstract: Interspecific variation in sperm size is enigmatic, but generally assumed to reflect species-specific trade-offs in selection pressures. Among passerine birds, sperm length varies sevenfold, and sperm competition risk seems to drive the evolution of longer sperm. However, little is known about factors favouring short sperm or constraining the evolution of longer sperm. Here, we report a comparative analysis of sperm head abnormalities among 11 species of passerine bird in Chernobyl, presumably resulting from chronic irradiation following the 1986 accident. Frequencies of sperm abnormalities varied between 15.7 and 77.3% among species, more than fourfold higher than in uncontaminated areas. Nonetheless, species ranked similarly in sperm abnormalities in unpolluted areas as in Chernobyl, pointing to intrinsic factors underlying variation in sperm damage among species. Scanning electron microscopy of abnormal spermatozoa revealed patterns of acrosome damage consistent with premature acrosome reaction. Sperm length, but not sperm competition risk explained variation in sperm damage among species. This suggests that longer spermatozoa are more susceptible to premature acrosome reaction. Therefore, we hypothesize a trade-off between sperm length and sperm integrity affecting sperm evolution in passerine birds.
authors.affiliation: Departamento de Anatomía, Biología Celular y Zoología, Universidad de Extremadura, , Avenida de Elvas s/n, 06071 Badajoz, Spain.
authors.forename: Ignacio G
authors.initials: IG
authors.lastname: Hermosell
authors.forename: Terje
authors.initials: T
authors.lastname: Laskemoen
authors.forename: Melissah
authors.initials: M
authors.lastname: Rowe
authors.forename: Anders P
authors.initials: AP
authors.lastname: Møller
authors.forename: Timothy A
authors.initials: TA
authors.lastname: Mousseau
authors.forename: Tomás
authors.initials: T
authors.lastname: Albrecht
authors.forename: Jan T
authors.initials: JT
authors.lastname: Lifjeld
mesh_terms: D000818:Animals; D005075:Biological Evolution; D048429:Cell Size; D047852:Chernobyl Nuclear Accident; D008297:Male; D008855:Microscopy, Electron, Scanning; D046109:Passeriformes / Q000502:physiology*; D013045:Species Specificity; D013077:Sperm Head / Q000528:radiation effects* / Q000648:ultrastructure; D013094:Spermatozoa / Q000002:abnormalities* / Q000166:cytology* / Q000528:radiation effects / Q000648:ultrastructure
keywords: acrosome; radiation; sperm evolution; sperm size